1. Field of the Invention
The invention relates to a catalyst composition suitable for hydrotreating, more particularly for hydrodesulphurisation and hydrodenitrogenation of hydrocarbon- containing feeds. The invention further relates to processes for the preparation and use of the catalyst composition.
2. Prior Art
In general, the object of catalytically hydrotreating hydrocarbon-containing feeds is the complete or partial removal of impurities. Common impurities are sulphur compounds and nitrogen compounds. The at least partial removal of such impurities from a feed will ensure that, when the final product is burnt, fewer sulphur oxides and/or nitrogen oxides harmful to the environment will be released. In addition, sulphur compounds and nitrogen compounds are toxic to many of the catalysts employed in the oil industry for converting feeds into ready-for-use products. Examples of such catalysts include cracking catalysts, hydrocracking catalysts, and reforming catalysts. It is therefore customary for feeds to be subjected to a catalytic hydrotreatment prior to their being processed in, say, a cracking unit. Catalytic hydrotreatment implies contacting a feed with hydrogen at elevated temperature and pressure in the presence of a hydrotreating catalyst. In this process the sulphur compounds and nitrogen compounds present in the feed are converted into readily removable hydrogen sulphide and ammonia.
In general, hydrotreating catalysts are composed of a carrier with deposited thereon a Group VI metal component and a Group VIII metal component. The most commonly employed Group VI metals are molybdenum and tungsten, while cobalt and nickel are the conventional Group VIII metals. Phosphorus may also be present in the catalyst. The prior art processes for preparing these catalysts are characterised in that a carrier material is composited with hydrogenation metal components, for example by impregnation, after which the composite is calcined to convert the metal components into their oxides. Before being used in hydrotreating, the catalysts are generally presulfided to convert the hydrogenation metals into their sulphides.
Because the requirements as to the legally permitted sulphur and nitrogen contents in fuels are becoming ever stricter, there is a continuous need for hydrotreating catalysts with improved activity. Further, at a given final sulphur content a more active catalyst will make it possible to operate under milder process conditions (energy saving) or to increase the life span of a catalyst between regenerations (cycle length).
Various efforts have been made in the art to provide hydrotreating catalysts with improved activity. A relatively new trend in this field is the use of additives. For example, Japanese patent application 04-166231 discloses a process for preparing a hydrotreating catalyst in which a support is impregnated with an impregnation solution comprising a Group VI metal component, a Group VIII metal component, and optionally a phosphorus component. The support is dried at a temperature of less than 200.degree. C., contacted with a polyol, and then dried again at a temperature below 200.degree. C. Japanese patent application 04-166233 discloses substantially the same process as the above-mentioned patent application, except that instead of a polyol an alkoxycarboxylic acid is used.
Japanese Laid -Open No. 1995-136523 teaches "burning" a support that has been impregnated with a solution of hydrogenation metal components at temperatures ranging from 200 to 400 .degree. C., followed by impregnation with an organic acid or polyhydric alcohol and then dried. This reference requires that the catalyst prior to the second impregnation not be a "conventional" catalyst. Thus, the catalyst of this reference prior to impregnation with an organic acid or polyhydric alcohol is prepared in a manner different than what is employed in making a conventional catalyst, whether the difference lies in the burning temperature or in the time of burning or in the combination of temperature and time.
Japanese patent application 06-339635 discloses a process in which a support is impregnated with an impregnation solution comprising an organic acid, Group VI and Group VIII hydrogenation metal components, and preferably a phosphorus component. The impregnated support is dried at a temperature below 200.degree. C. The dried impregnated support is contacted with an organic acid or polyol, after which the thus treated support is dried at a temperature below 200.degree. C.
Japanese patent application 06-210182 discloses a process for preparing a catalyst in which a boria-alumina support comprising 3-15 wt. % of boria is impregnated with an impregnation solution comprising a Group VI metal component, a Group VIII metal component, and a polyol. The impregnated support is dried at a temperature of 110.degree. C. to form a catalyst.
European patent application 0 601 722 describes a process for preparing a catalyst in which a gamma-alumina support is impregnated with an impregnation solution comprising a Group VI metal component, a Group VIII metal component, phosphoric acid, water, and diethylene glycol. The impregnated support is dried at a temperature of 100.degree. C. The catalysts are presulfided with a Kuwait straight-run gas oil containing 1.15 wt. % of sulphur and 3% butane thiol.
Although the above catalysts do indeed show improved hydrotreating activity as compared with conventional hydrotreating catalysts which do not contain an additive, this improved activity will only appear when the catalyst is used for the first time. Regeneration of the catalyst by burning off coke results in removal of the additive from the catalyst, so that the improvement in activity is lost in the further catalyst life cycles.
U.S. Pat. No. 4,530,917 describes a process in which a conventional hydrotreating catalyst is contacted with an additive, but in this patent the additive is present in a presulfiding solution which contains a polysulfide as sulfiding agent.
U.S. Pat. No. 5,032,565 describes a process for reducing catalysts comprising a Group VIII metal by contacting them with a reducing agent which may be an alcohol or polyalcohol. It is expressly stated that this process is applicable to catalysts which normally are not sulfided because sulphur is a poison to this type of catalyst